The present invention relates in general to an apparatus for powering X-ray tubes. More particularly, the invention relates to a discharge module for a cable connecting a high-voltage power supply and an X-ray tube which discharges any capacitive voltage remaining on the cable between X-ray exposure frames.
In a conventional X-ray tube, X-rays are produced by generating electrons by thermionic emission from a tungsten filament (cathode). The electrons are then accelerated to an anode (which may be rotating for wear averaging purposes) to generate the X-rays. The emission intensity of the tube is controlled by the filament current and by the high-voltage potential difference between the anode and cathode.
Precise control of the power supplied to an X-ray tube is important to insure proper imaging for diagnostic purposes and to avoid unnecessary exposure of the patient to X-ray radiation which does not produce a usable image. For example, when an X-ray tube is being used for applications such as cardiac angiography, the X-ray tube is operated in relatively short bursts at a relatively high frequency in order to obtain clear images and to be able to monitor heart activity and detect any abnormalities. Typically, the tube is operated at approximately 8 ms bursts. Where the X-ray image is to be recorded by a television camera, the exposure is further synchronized with the 60 Hz sweep rate of the TV camera so that a coherent picture is produced, i.e., at rates of 60, 30, 15 or 7.5 frames per second.
The relatively small X-ray tube current produced with pulsed fluroscopy does not sufficiently discharge the capacitance of the high-voltage cables connecting the power supply and X-ray tube between exposure frames. The "tail" on the power supply output waveform produces unwanted soft radiation which adds to the patient dose and does not improve the image. It would thus be desirable to provide a high-voltage power supply for an X-ray tube which produced substantially rectangular waveforms without a trailing tail of unwanted soft radiation.